This invention relates to a vehicle mounted a.c. generator adapted to be driven by the engine of the vehicle, and particularly to an improved cooling system thereof.
A cross section of a conventional vehicle mounted a.c. generator is shown in FIG. 1, in which a pulley 2 and a rotor 3 are secured to a rotary shaft 1. The rotor 3 is composed of a rotor core 4 mounted on the shaft 1, a magnetic pole member 5 having a plurality of angularly spaced teeth 5a formed peripherally thereof, a support ring 6 of non-magnetic material fixedly secured to an inner periphery of the teeth 5a, and an opposite magnetic pole member 7 fixedly secured to the support ring 6 and having a plurality of angularly spaced teeth 7a which are interleaved with the teeth 5a. A stationary exciting core 8 is arranged between the core 4 and the member 7 and defines air gaps therewith, and supports an exciting coil 9.
The generator further includes a stator core 10 which supports a stator coil 11 in slots thereof, a front bracket 12 which supports the shaft 1 through a bearing 14, outlet holes 12a formed in the bracket 12, and a rear bracket 13 for supporting, together with the front bracket 12, the stator core 10 and the shaft 1 through a bearing 15. The bracket 13 also fixedly supports the core 8, and has inlet ports 13a for cooling air. A rectifier 16 converts a.c. power produced in the stator coil 11 into d.c. power. A voltage regulator 17 detects the generator voltage and controls the exciting current to thereby regulate the terminal voltage to a predetermined value. A fan 18 is fixed to the shaft 1.
In this conventional a.c. generator, the shaft 1 is rotated by the engine through a belt and the pulley 2. Upon rotation of the shaft 1, an a.c. voltage is induced in the stator coil 11 which is rectified by the rectifier 16 and regulated by the voltage regulator 17, the resultant d.c. voltage being supplied to the exciting coil 9 and to a load such as a battery.
Cooling air drawn through the inlet ports 13a of the rear bracket 13 by the rotation of the fan 18 cools the interior of the generator, and is discharged through the outlet ports 12a of the front bracket 12.
In such a generator, heat generated by the exciting coil 9, stator coil 11, bearings 14 and 15 and voltage regulator 16 housed in the bracket 13 is discharged by the air flow mentioned above. However, it is usually insufficient to cool the inside of the bracket 13 by means of the fan 18. In order to obtain a sufficient cooling effect it is possible to use a larger fan. However, such a large fan is noisy. Further, since the air used to cool the generator tends to degrade the insulation of various portions thereof, the use of an air coolant passing through the inside of the generator should be minimized. In addition, the power required to drive such a large fan is considerable.